In comparison with incandescent and halogen lamps, LEDs have higher efficiency and longer lives. With the recent increase in the intensity of white LEDs, active studies have been made on application of the white LEDs to illumination purposes. Among various point light sources, LEDs are expected, owing to their property, to replace halogen lamps which are currently in wide use for spot lighting at shops, museums, and showrooms.
Unfortunately, however, a conventional white LED produces, on the irradiated surface, a beam spot distorted into a square shape. For application to the illumination purpose, the beam spot distortion needs to be corrected. A white LED produces a square-shaped beam spot because an LED chip (semiconductor light emitting element) constituting the white LED is rectangular and light is emitted mainly through a square-shaped surface thereof (see, for example, JP 2001-15817-A).
Ideally, it is desirable to produce LED chips having a cylindrical shape. Yet, the chances are extremely small in view of productivity. The reason lies in the dicing process, which is the final stage of LED chip manufacturing, to cut a wafer into separate LED chips with a diamond wheel. It is practically impossible to cut the wafer into cylindrical-shaped LED chips having a diameter on the order of hundreds microns. A rectangular LED chip may be ground into a cylindrical shape, which is also virtually impractical in view of the chip size.
In view of the above, an LED chip having the shape of a substantially regular hexagonal prism is suggested for ensuring both high productivity and a close-to-circle beam spot. LED chips having the shape of a substantially regular hexagonal prism can be manufactured with efficiency using the technique disclosed in JP 11-340507-A.
Here, with reference to FIG. 31, a description is given to the manufacturing method of LED chips having the shape of a substantially regular hexagonal prism, disclosed in JP 11-340507-A.
A single crystal substrate 300 has a hexagonal closest-packed lattice (hereinafter, simply “HCP”) crystal structure, such as GaN or SiC, having the (0001) plane on main surfaces. As shown in FIG. 31A, the HCP single crystal substrate 300 can be cleaved along the [1-210], [2-1-10], and [11-20] orientations. One of the crystallographic orientations coincides with an orientation flat 302 of the single crystal substrate. For example, in the case where the [1-210] orientation is parallel to the orientation flat 302, the [2-1-10] and [11-20] orientations extend at 60° and 120° to the orientation flat 302, respectively.
In view of the above, after forming such components as electrodes and a semiconductor multilayer structure containing a light emission layer (none of the components are illustrated) on the single crystal substrate 300, cleavage guide grooves 304 are formed in the [1-210], [2-1-10], and [11-20] orientations indicated by doted lines in FIG. 31A. With the guide grooves 304, the single crystal substrate 300 is partitioned into hexagonal areas 306 each of which will be later formed into an LED chip. By cleaving along the guide grooves 304, the single crystal substrate is divided into separate LED chips.
According to the above method, LED chips having the shape of a hexagonal prism are manufactured with efficiency. In addition, by cleaving along the crystallographic planes, chipping and cracking of the semiconductor multilayer structure at the time of dicing are suppressed.
Although the technique disclosed in JP 11-340507-A ensures improved productively, there is a problem that the single crystal substrate is not fully used. More specifically, as shown in FIG. 31B, which is a partial enlarged view of FIG. 31A, portions of the semiconductor multilayer structure grown in substantially regular triangle areas 308, which are enclosed with the substantially regular hexagonal areas 306 to be later formed into LED chips, are wasted without being used.
In view of the above problem, the present invention aims to provide a semiconductor light emitting device which, as a whole, has the shape of a substantially regular hexagonal prism and yet allows the best possible use of the single crystal substrate with minimum wastage. The present invention also aims to provide an illumination module and an illumination apparatus both having the semiconductor light emitting device. The present invention also aims to provide a method for manufacturing the semiconductor light emitting device and a method for manufacturing a semiconductor light emitting element having the shape of a substantially regular hexagonal prism.